Should I use a Cartridge Filter or a Sand Filter in my Hot Tub?

Cartridge Filter

Cartridge filters and sand filters are two of the most popular methods for filtering water in a hot tub. There is no right answer to whether you should use one or the other, but there are some important differences between them that you should be aware of before making your choice:

Find out more about these points before deciding which type of system makes better sense for you overall. Then continue reading for details on how to get started with each type of filter.

What is a cartridge filter?

A cartridge filter is typically a pleated polyester pad with an ABS plastic housing around it, surrounded by an inflated bladder. It attaches to the back of your hot tub and uses a simple system of hollow tubes, water pressure, and gravity to push dirty water through the filter before returning it into the spa.

What is a DE Filter?

The most common type of cartridge filters (also called diatomaceous earth (DE) filters) use DE powder as their filtration media. This absorbent dust is made from crushed fossilized shells that naturally attract dirt particles in water when they come into contact with each other. Think about how mud gets dirty after you walk through grass or on a beach: that’s because tiny dirt particles become trapped between rocks and sandy areas during high water. A DE filter works much the same way when water passes through it: dirt and debris are trapped in between the thousands of tiny holes that make up each grain of diatomaceous earth.

How Does a Cartridge Filter Work?

A cartridge filter works by creating a barrier through which bacteria can’t pass. This isolation prevents “friendly” bacteria from mixing with dirt in the water, thus preventing any chance of growth within the hot tub environment. The result is cleaner water without any “bits” in it.

What sizes do Cartridge Filters Come In?

Cartridge filters come in different sizes to accommodate hot tubs of all shapes and sizes.

The cartridges themselves can also vary in size; many are 4″ x 23″, but some are as large as 11″ x 40″. The dimensions vary depending on how much water is actually in the tub.

For most of our DIY built Hot Tubs, a 50 square foot filter is going to be more than enough to filter our tubs.

How Long Do Cartridge Filters Last?

The life expectancy of your filter depends on how often you use the hot tub and the type of water you put through it, such as if you like to run it with fresh water or use salt water in it. If you have hard well water, your filter will need to be replaced more often than if you used soft city water.

Maintaining the cartridge is important if you want it to last as long as possible. You can do this by ensuring that hot tub chemicals are kept at the correct levels and that your pH balance is good, alkaline and not acidic. Using a salt treatment system can also increase the life of the filter cartridge by making it less prone to clogging up with minerals from the spa.

Cartridge Filter Care

It’s important to maintain cleanliness of your filters because a dirty filter won’t work properly, even if you keep the right amount of chemicals in your spa. At least once a month you should remove the filter and let it soak in cartridge cleaner overnight. Following that, you are going to want to give them a good blasting with the power washer.

What is a Sand Filter?

Sand filters are the most effective way to clean your spas water. Originally developed for swimming pools, they contain between 150 and 200 lbs of sand in a drum-like container. The filter is installed underneath the spa (down-flow) so that the water has to pass through all the beads before entering into your spa tank.

This filtering method requires you to occasionally backwash or rinse out the sand, since it will eventually be clogged up with minerals and other impurities picked up from your hot tub water.

Sand Filter

How often do you need to change the sand?

You should change the sand in your filter about once a year. It is recommended that you add a couple of inches of sand at least once every season, or more often if you use your hot tub regularly. The proper amount of backwash water to run through the filter must reach past the top layer of sand by 3/4″.

When you consider how much your spa costs to heat up, it makes sense to have an effective way to clean its water and extend the life span of your hot tub too.

The cartridge filters are less abrasive than Sand Filters . They contain less than a pound of granulated activated carbon and uses cartridges (like those found in spray bottles) with larger pores than sand filters have.

How do you clean a Sand Filter?

The sand filters are quite easy to clean. To backwash the filter, simply turn on the house water supply and let it flow through the system for about 5 minutes. Other than that, there is not a great deal you need to do with a sand filter. For this reason, Sand Filters are quite popular with pool owners as they are such low maintenance.

When Should I use a Sand Filter?

If you have ever had problems with high chlorine levels or an excess of heavy metals in your drinking water, then you probably already do not drink tap water without some sort of filter on, then sand filters are for you.

Also, sand filters are much more suited to larger bodies of water such as swimming pools.

Which Hot Tub Filter to use?

If you are looking for a filter that is very inexpensive and easy to maintain, then go with the cartridge or diatomaceous earth filter. Most spas will use this type of filter due to their low price point.

If you are worried about excessive chlorine levels in your water, then also consider a “water clarifier” which can be used along with these filters. They cost more than the other two types of filters but work very well when combined together.

For me, cartridge filters are the way to go in your DIY Hot Tubs. If you are building a spool, cocktail pool or swimming pool, then head down the sand filter route.

Sand filters may be less maintenance but the initial cost is much higher than theit cartridge filter counterparts.

Happy Hot Tubbin’


Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi

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